A calendar mechanism of this type is described, for example, in U.S. Pat. No. 7,532,546. This calendar mechanism comprises, in particular, a tens disc bearing the numerals 0 to 3, and two units discs, an upper disc bearing the numerals 0 to 4, and a lower disc bearing the numerals 5 to 9. Due to this arrangement, the change of date from the 28th to the 29th February or at the end of months of 30 days requires one or more intermediate jumps of one or both discs to display the first day of the following month. This therefore leads to a lack of precision in the calendar display as the date changes.
Further, the date is displayed by means of a tens disc and a units disc which are on two different levels on 15 out of 31 days, i.e. close to half the month. This difference in height between the units numeral and the tens numeral gives an unattractive visual appearance. Further, as the date changes, especially from the 31st to the 1st, only the tens disc moves so that the change of date is not clearly displayed.
There are also continuous-type calendar mechanisms, but they have the drawback of leaving the date display imprecise for a certain time as the date changes, and especially as the month changes.